The major research objective of this proposal is the further delineation of certain structural-functional relationships in various regions of the mammalian renal tubule. Specifically, by using a combined morphological- physiological investigative approach, efforts will be directed toward determining the cellular and subcellular mechanisms that control sodium reabsorption along the nephron, establishing the sites of bicarbonate reabsorption and hydrogen ion exchange within the distal nephron, examining the phagocytic capabilities of the proximal convoluted tubule, investigating the influence of bilirubin on mechanisms of urinary concentration and exploring the factors responsible for post-obstructive diuresis after short term ureteral obstruction. Investigative techniques to be employed in the various phases of this proposal include micropuncture, microperfusion, electron microscopy and autoradiography. Experimental models to be utilized include the toad bladder, the Gunn rat and the isolated perfused tubule.